At present, in the high frequency switch power supply system, the industrial frequency alternating current (ac) is generally converted to the direct current by the rectifying device and then is delivered to the subsequent circuit. The most commonly used rectifier device is the bridge rectifier circuit, because the subsequent circuit usually contains a filter capacitor with large capacitance, a anti-surge circuit must be added into the input circuit to avoid the surge current caused by quick charge of the filter capacitor during the starting of electrical equipment which leads to a damage of the rectifying device, filter capacitor or other device. To this, the simplest method of preventing a surge is implemented by adding a current limiting resistor (it is usually a negative temperature coefficient thermistor) in series with the input circuit, in order to prevent the influence of the current limiting resistor on the conversion efficiency, usually a switching device (it can be a relay or semiconductor switch) is connected to the current limiting resistor in parallel.
In FIG. 1, the circuit with the reference number 100 is the bridge rectifier and surge control circuit in the prior art. At the starting moment of the electric equipment, the alternating current (ac) flows through the fuse F1, EMI filter network 200 in the electric equipment, then is limited by a current-limiting resistor Rt (the control switch 101 is off), is rectified by the rectifier bridge BD, and charges a filter capacitor C. When the electric equipment enters into the stable working state, control switch in parallel with the current limiting resistor Rt is closed to eliminate the influence of the current limiting resistor Rt on the conversion efficiency.
During rectifier procedure, the bridge rectifier and surge control circuit in the prior art rectifies the current through two series rectifier diode in each half cycle. Because the rectifier diode has high positive voltage drop (typically about 1.2 V), so the power loss brought by the bridge rectifier takes a larger proportion in the whole power consumption, which increases the power consumption of the entire circuit. In addition, the cost of the control switch in parallel with the current limiting resistor is high, if the control switch is a semiconductor switch, it will bring a large extra power consumption, and if the control switch is a relay, although the relay has small power consumption which can be ignored, the large volume of the relay leads to an increase of the entire volume of the bridge rectifier and surge control circuit, which goes against the miniaturization of the circuit. Therefore, the bridge rectifier and surge control circuit in the prior art has the problem of high power consumption, high cost and large volume.